Unusual central heating bypass valve

I have a central heating system using a Glowworm EnergySaver 60 boiler (open vent configuration), grundfos pump and a microbore network of pipes (although the max run of microbore from the main 22mm send/return pipes to any given radiator is only 1 meter). All radiators except one feature TRVs. As would be expected, the radiator without the TRV is permanently fully on.

While investigating flow issues I noted that there is a valve between the flow and return pipes directly after the pump. This valve is not a normal bypass valve (that operates to maintain minimal flow only when radiators are shut off) but is a simple tap that can be opened closed like any other.

When I tried this tap I found that it had been left partially open, allowing a reasonable amount of heated water to flow directly from the send to the return pipe without passing through either the CH or DHW circuits. Is there any reason why this valve should be there and why it would have been left partially open?

Given that we have been experiencing limitted flow to the most distant radiators (despite carefully balancing the system and running the pump flat out) and that the boiler seems to 'kettle' very easily, I am keen to close this valve. However, without knowing what it is for, I am nervous to adjust its setting.

Any thoughts?

Thanks,

iep

as far as im aware, 'in the old days' rather than an automatic bypass, a tap was used.

this allowed a amount of water to bypass all the time, just in case all of the rads where turned off.

which seems odd as u have a rad with no trv... unless they all had trvs at one point.

how old is the pipe work?

This valve is more than likely a bypass. Do you have a y plan or s plan system ? If y plan you can shut this as you have a permanent circuit anyways and monitor how the boiler reacts when it shuts down. you say it kettles easily enough , there maybe a more inherrant fault on the system.

Pump over-run faulty

Pump faulty (which may account for poor performance and kettling)

Sludge in system particularly in manifold for microbore

Thanks for the responses. The system is quite old (maybe 30 years old) with the boiler and pump having been replaced about 8 years ago (according to receipts). There is no manifiold in the system per say because the house is very long and narrow. As a result, the fitter simply installed two 22mm pipes (on send, one return) along the entire length of the house. Each radiator simply taps off this pipe where it passes each room. So, there is no obvious location for the sludge to accumulate (as there can be in system s with a single manifold).

I think I have an S plan system as there are two seperate 2 port valves below the pump (one for CH, the other for the Hot water cylinder).

As far as I can tell from the wiring though (and I've had a good look at this), the single 'call for heating' or 'call for hot water' wires from the control unit enable the valve, boiler and pump simultaneously. I cannot see an obvious case where the valve could be closed while the boiler pump would remain on. However, maybe I am missing something?

ducatikid, could you explain how the pump over-run works? For the record, the ketting sound only occurs from about 10 seconds before the boiler shuts itself off (bear in mind the boiler thermosta is only set to mid). We are also in a very saft water area so internal scaling etc on the manifold is very unlikely.

I think the pump is in decent health as it is very quiet. The only failed pump I have seen was very noisy although maybe they don't all fail this way.

Cheers,

iep

It's a manual bypass valve. The Installation Instructions say:

When commissioning the system the boiler should be fired with the bypass fully closed on full service, that is, central heating and domestic hot water. The system should then be balanced, adjusting the pump and lockshield valves as necessary to achieve flow rates, refer to Section 2.4 (*).

Having achieved a satisfactory condition, operate the boiler with the bypass closed on minimum load, normally central heating only with one radiator operating in the main living area. The valve should be opened gradually to achieve the appropriate flow rate as quoted in Section 2.4(#). If necessary readjust the pump.

Under NO circumstances should this valve be left in the FULLY Closed position.

(*) The first flow rate is 23 litres per minute, which means a temperature drop across the boiler of 11.

(#) The second flow rate is 17 litres/min, which means a temperature drop of 15C across the boiler.

How to balance a CH system

The pump over-run does exactly what it says on the tin so to speak. It will continue to run after all thermostats are satisfied or timer is switched off to dissipate heat from the boiler. This prevents scaling of the boiler or the boiler going to lockout on the high limit stat.
Back to this valve as you have 2 ports you cannot shut this valve or the boiler will sound like it wants to jump off the wall when it the thermostats satisfy or timer switches off. The energy saver is a low water content and really needs to get rid of that heat fast. it sounds like the pump over run is wired correctly. Minor kettling in this boiler is not unusual so don't worry too much about that , however to get back to your fault , I would say if balancing the system has been tried and not worked (btw have you noticed a balancing valve on the return from the cylinder?) How far open is the bypass valve? You can try and close this down a bit but as I said earlier , too much and the boiler will let you know!

Just to add something else re the problem. Has the system worked fine previously and has just gotten progressively worse? If so then I would certainly look at the pump and possible sludge problems. a treatment of something like x400 is cheap enough and may reap rewards. Good luck!

ducatikid. Just to get this straight then:

Since the 2 port valves are driven directly from the central heating controller, I guess they close immediately when the central heating call signal goes low (there is only one wire from the control unit that 'calls for heat'). However, the pump is driven from the boiler's control board so I guess this is where the overun circuit lives (basically maintains supply to the pump for a short period after the 'call for heat' signal goes low).

In that case, I can see why the bypass valve would be needed since the pump will have nowhere to pump to when the control unit switches off the heating (since both 2 port valaves will be closed if the call for HW is also low).

Is that about right?

For the record, we only moved into the house 1 month ago and my suspicion is that the heating has perfromerd poorly for some time. I am nervous about using a sludge treatment as I have never flushed/filled a central heating system beofre and gather that I owuld need to do this after using the treatment.

*****

D_Hailsham, thanks for the info. It looks like I may not have correctlty balanced the system as I did not know about the bypass valve when I started. Is balancing simplified by the addition of an automatic bypass valve?

It certainly seems desirable to me that the bypass valve would be fully closed when the system is initially switched on and I guess an automatic valve would allow that.

Cheers,

iep

D_hailsham, Just found the section in the Energysaver manual that you are referring to (ie the 23 litres per min and 17 litre per min figures). How are you converting these numbers into temp drop figures. This seems to be a very useful trick.

Cheers,

iep

ducatikid, I just realised my system does not have full pump overrun protection.

The boiler itself does have a pump overrun circuit but this only works where the boiler's internal thermostat has shut the system down (ie when it thinks the water from the return pipe is hot enough). In this case, it shuts off the boiler and keeps the water pumping for a short while.

However, where the timer switch and/or room thermostat have shut the boiler down, all power is removed from the boiler and therefore also the pump. This is more or less as per the wiring diagram below:

http://www.plumberparts.co.uk/wp-content/uploads/2009/11/S-Plan-Wiring-300x278.gif

This should mean that there is no way that the pump can be run when the both the zone valves are switched off (unless the valve is broken).

This explains why the pump did not try to jump off the wall when I experimentally tried closing the bypass valve.

However, now knowinng that the valve is there to protect the system when the TRVs shut down multiple radiators, I realise I need ot live it open.

Cheers,

iep

your boiler should have a permanent live and a switched live connected to the terminal strip in the boiler, then your pump overrun will work correctly.

Is your pump wired into the boiler?

Does the permant live stay "live" when the programmer switches off the water and heating?

X200 in the system might improve the kettling situation but if its sludged then X400 or X800 should be used first and drained and flushed away before adding the X200.

Tony

okay, a bit more research shows that the cowboy who installed my boiler wired the switched live connection to the boiler using a length of green/yellow earthing wire. So, the boiler does have a permanent and switched live. So, pump overrun will sometimes happen and the bypass valve must be set accordingly.

My current thinking is to locate (or install) a drain point, drain down the system an fit a proper automatic bypass valve instead of the gate valve that is currently installed.

Cheers,

iep

iep said:

D_hailsham, Just found the section in the Energysaver manual that you are referring to (ie the 23 litres per min and 17 litre per min figures). How are you converting these numbers into temp drop figures. This seems to be a very useful trick.

Click to expand...

Flow rate (litres/sec) =kW Output ÷ (4.18 x Temp Diff)

or

Temp Diff = kW Output ÷ (4.18 x Flow Rate)

The constant (4.18) is an approximation to Joules Equivalent.